Taphonomic bias

Systematic distortion of biological information through differential preservation and recovery. teeth and delicate soft tissues need not have the same probability of entering the fossil record; even a locally buried assemblage can therefore give a biased account of its living community.

Erroneous placement toward the base of a lineage when loss of diagnostic characters through carcass decay is interpreted as an ancestral biological absence. Coding unobservable characters as unknown and comparing preservation across specimens can reduce the problem.